1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine and more particularly to a control apparatus, for an internal combustion engine, that is provided with a function capable of appropriately estimating and updating the concentration of alcohol in a fuel for the internal combustion engine that utilizes an alcohol-containing fuel.
2. Description of the Related Art
There exists an automobile that is referred to as a so-called flexible fuel vehicle (referred to as FFV, hereinafter), which can travel with a mixed fuel composed of alcohol and gasoline at various ratios, in addition to gasoline. Alcohol is different from normal gasoline (mixed fuel) in the amount of contained carbon atoms; therefore, in supplying a mixed fuel composed of alcohol and gasoline to an internal combustion engine utilized in an FFV, it is required to adjust the fuel injection amount, in accordance with the alcohol concentration value of the fuel.
Accordingly, among such FFVs, there have been known a control apparatus in which the alcohol concentration value of a fuel is detected by an alcohol concentration sensor disposed in the fuel tank and a control apparatus in which an alcohol concentration is estimated through the correlation between the alcohol concentration value and the average value of air-fuel ratio feedback correction coefficients that are calculated based on the air-fuel ratio in exhaust gasses. Moreover, as disclosed in Japanese Patent Application Laid-Open No. H9-60003 and Japanese Patent Application Laid-Open No. 2004-285971, there have been known control apparatuses that prevent the drivability (driving performance) and the exhaust gas performance from being impaired even in the case where the alcohol concentration sensor is abnormal.
That is to say, Japanese Patent Application Laid-Open No. H5-60003 proposes a method in which, in the case where an abnormality occurs in an alcohol concentration sensor, by forcibly giving an arbitrary concentration value before feedback control is started and detecting the optimum driving condition based on the value of change in the engine rotation speed, the optimum concentration value is estimated before feedback is started even in the case where an abnormality occurs in the alcohol concentration sensor.
Additionally, Japanese Patent Application Laid-Open No. 2004-285971 proposes a method in which, in the case where the control apparatus for an engine is replaced, by utilizing a first fuel property representative value given from the outside and estimating/updating the alcohol concentration value, there is prevented deterioration in the movement performance of the internal combustion engine such as being unstartable or deterioration in the exhaust gas performance.
However, in the case of Japanese Patent Application Laid-Open No. H5-60003, when, during concentration estimation before the feedback control (while the loop is opened), the feedback control is established, the foregoing concentration estimation is interrupted and feedback-controlled concentration estimation is started. In this situation, in the case where the feedback control is out of order, e.g., an abnormality exists in the feedback system, the open-loop concentration estimation is not completed and the feedback-controlled concentration estimation is not correctly performed, whereby an erroneous alcohol concentration value is estimated/updated; as a result, there has been a problem that, during open-loop driving, the drivability (driving performance) and the exhaust-gas performance of the vehicle are adversely affected.
Moreover, also in the case of Japanese Patent Application Laid-Open No. 2004-285971, there has been a problem that, in the case where an alcohol concentration value is updated during the feedback control and an abnormality exists in the feedback system, an erroneous alcohol concentration value is estimated/updated, as is the case with Japanese Patent Application Laid-Open No. H5-60003. Still moreover, because, as a control value, an alcohol concentration value is updated and utilized based on a value given from the outside, there has been a problem that, when being erroneously updated, the alcohol concentration value cannot be restored. In other words, in the case where, because there actually exists no problem in an unupdated alcohol concentration value, e.g., there exists a problem in an item, other than the alcohol concentration value, such as a device, e.g., an injector or an ignition system, the driving condition of the vehicle does not become optimum even through the alcohol concentration value is updated, there has been a problem that, because the alcohol concentration value cannot be restored, solving of the problem with regard to the vehicle drivability is hindered.